1. Field of the Invention
The invention relates to fixed ratio traction roller transmissions in which the contact forces applied to the traction surfaces which are in engagement with each other for the transmission of movement are dependent on the torque transmitted through the transmission.
2. Description of the Prior Art
Traction roller transmissions in which large contact forces are applied to prevent slippage of the rollers are described for example by Harold A. Rothbart in "Mechanical Design And Systems" Handbook pages 14-8 and 14-9, McGraw-Hill, New York, 1964. In the relatively simple arrangements of FIGS. 14.6 and 14.7 wherein the outer rings are slightly undersized to compress the roller arrangements, the surface pressure on the traction surfaces is always the same, that is, it is always high independently of the torque transmitted through the transmission. Various transmission arrangements are also known in which the contact pressure of the traction surfaces is dependent on the size of the torque transmitted through the transmission for example as in those shown on page 14-8 of said handbook. Other transmissions of this type are shown in U.S. Pat. Nos. 771,541; 1,212,462; 1,704,205; 1,956,934; 3,610,060 and Swedish Patent No. 281,542.
In the arrangement shown in U.S. Pat. No. 771,541 the variable compressive forces are obtained by an outer ring structure so arranged that the ring is compressed when a torque is transmitted through the transmission. However, the arrangement requires sliding surface areas which are difficult to manufacture or complicated lever arrangements which amplify the reaction forces of the transmission to provide sufficient compression of the outer ring for its engagement with the traction rollers. Furthermore, there is a discontinuity in the outer ring structure which, with the large forces taken up by the ring structure, may well lead to premature failures.